Another model of anaesthesia machine that works using draw-over principles is the Universal Anaesthesia Machine (UAM) (Fig 1).

• The green bag works on the same principle as the DPA portable device and acts as a reservoir for oxygen
• If there is no flow, room air is drawn in through the air inlet valve
• If the flow selected on the rotameters is less than the patient's minute volume the pressure in the backbar stays ambient
• If the flow from the rotameters is more than the patient's minute volume the pressure increases to 5 cmH₂O and excess gas escapes from the pressure relief valve (Fig 2)
• A collapsing or distended reservoir bag will indicate which is the case